Body fat of stock-type horses predicted by rump fat thickness and deuterium oxide dilution and validated by near-infrared spectroscopy of dissected tissues1

Abstract

Body condition score and percent body fat (BF; %) of horses are positively correlated with reproductive efficiency and are indicative of metabolic issues. However, BF in horses may be poorly predicted because current procedures are either subjective or dependent on one anatomical location. Therefore, the objectives of the current study were to compare 2 methods of predicting BF using rump fat thickness (RFT) and deuterium oxide (DO) dilution with actual tissue fat analysis by near-infrared spectroscopy (NIRS) in stock-type horses and to identify the relationship between BF and BCS. Twenty-four stock-type horses were selected to be humanely euthanized based on 3 primary criteria: geriatric, crippled, and/or unsafe. Approximately 20 h before slaughter, horses were weighed and BCS assessed to be 1 ( = 1; 433 kg), 2 ( = 1; 415 kg), 3 ( = 1; 376 kg), 4 ( = 7; 468 ± 13 kg), 5 ( = 10; 455 ± 11 kg), and 6 ( = 4; 493 ± 12 kg) and RFT was measured using ultrasonography. Blood samples were collected immediately before and 4 h after DO infusion (0.12 g/kg BW). Deuterium oxide concentration of plasma was determined by gas isotope ratio mass spectrometry. Horses were housed in a dry lot overnight before being individually sedated (1.1 mg xylazine/kg BW) and anesthetized using a jugular venipuncture (2.2 mg ketamine/kg BW), and potassium chloride (KCl) solution was administered to cease cardiac function before exsanguination. After euthanasia, horse carcasses were processed and dissected and tissues were collected for NIRS analysis. Body fat predicted by DO dilution was correlated with BF measured by NIRS analysis on various weight bases ( = 0.76 to 0.81, < 0.001), whereas no correlation was observed for BF predicted by RFT. A paired -test indicated that both DO dilution and RFT overestimated BF by 2.48 to 3.26% ( < 0.001) and 5.81 to 6.59% ( < 0.001), respectively, compared with NIRS analysis. Body condition scores affected BF measured by NIRS analysis ( ≤ 0.038) and predicted by DO dilution ( < 0.001) and RFT ( = 0.042). The current study provided evidence that DO dilution was a better prediction method for BF than RFT and that BCS may serve as a BF predictor in stock-type horses.

Relationship between live body condition score and carcass fat measures in equine

“…Our study agrees with previous data ( Westervelt et al, 1976 ; Henneke et al, 1983 ; Ferjak et al, 2017 ), which indicated that measures of body fatness correlate with the lipid content of horses. Our measure of percentage KPH fat is in alignment with the increasing percentage of body fat assessed in BCS 4 to 6 equine as reported by Ferjak et al (2017) .…”

“…Our study agrees with previous data ( Westervelt et al, 1976 ; Henneke et al, 1983 ; Ferjak et al, 2017 ), which indicated that measures of body fatness correlate with the lipid content of horses. Our measure of percentage KPH fat is in alignment with the increasing percentage of body fat assessed in BCS 4 to 6 equine as reported by Ferjak et al (2017) . Additionally, Gentry et al (2004) and Indurain et al (2009) indicated that both visual and ultrasound measures of body fat were correlated with fatness of horses, and Ferjak et al (2017) suggested that visual and palpable appraisal of the BCS system might be useful in body fat prediction modeling.…”

“…They reported D 2 O dilution-derived estimates of total body water and body fat to values obtained from proximate analysis and carcass dissection were strongly correlated to the proximate analysis of the whole body and of dissected white adipose tissues. Ferjak et al (2017) also observed a strong correlation between D 2 O prediction of body fat and body fat as measured by carcass dissection and near-infrared spectroscopic analysis. The authors further reported that of the 24 stock-type horses with BCS of 4, 5, and 6, those with a BCS of 6 had greater body fat as compared with those with BCS of 4 or 5.…”

“… Westervelt et al (1976) suggested that measuring rump fat thickness using ultrasound was a useful method to estimate body fat in horses and ponies. Cavinder et al (2017) stated that although ultrasonic measurements have been used in several studies to determine body fat ( Cavinder et al, 2007 ; Cordero et al, 2013 ; Ferjak et al, 2017 ), the reliability of this method has been questioned due to fat deposits varying among individual horses. The most commonly cited and predominant live body composition tool for horses is the body condition scoring (BCS) system developed by Henneke et al (1983) , who reported that calculated percentage body fat, as measured by ultrasound-measured rump fat thickness ( Westervelt et al, 1976 ), was positively correlated ( r 2 = 0.65) to BCS.…”

Development of a mathematical model for predicting digestible energy intake to meet desired body condition parameters in exercising horses

“…The limited number and variety of subjects utilized when validating the method has led researchers to search for a non-invasive whole body assessment, such as isotope dilution (Dugdale et al, 2011). Ferjak et al (2017) found that equine BF assessment using deuterium oxide was more strongly correlated to actual BF measured postmortem than was BF extrapolated from rump fat thickness (Ferjak et al, 2017). Previous studies have reported that the relationship between BCS and BF extrapolated from RFT is positive and linear (Henneke et al, 1983;Cordero et al, 2013); while postmortem evaluations have yielded an exponential relationship to actual BF (Martin-Rosset et al, 2008;Dugdale et al, 2011).…”